Added extra buttons:

- Implemented retry button*
- Escape on mode select sends you to title screen
- Escape on title screen closes the game
- Added "Exit Game" entry on title screen, closes the game when selected

*Pardon my angry comment in `scene/game.lua`.

scene/input_config.lua

@@ -15,6 +15,7 @@ local configurable_inputs = {
     "rotate_right2",
     "rotate_180",
     "hold",
+    "retry",
 }
 
 function ConfigScene:new()